EP0600491A2 - Method and apparatus for testing fluid pressure in a sealed vessel - Google Patents
Method and apparatus for testing fluid pressure in a sealed vessel Download PDFInfo
- Publication number
- EP0600491A2 EP0600491A2 EP93119457A EP93119457A EP0600491A2 EP 0600491 A2 EP0600491 A2 EP 0600491A2 EP 93119457 A EP93119457 A EP 93119457A EP 93119457 A EP93119457 A EP 93119457A EP 0600491 A2 EP0600491 A2 EP 0600491A2
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- EP
- European Patent Office
- Prior art keywords
- fluid
- vessel
- frequency
- pressurized fluid
- natural frequency
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M99/00—Subject matter not provided for in other groups of this subclass
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
- G01L11/04—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by acoustic means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0001—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means
- G01L9/0008—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M17/00—Testing of vehicles
- G01M17/007—Wheeled or endless-tracked vehicles
- G01M17/0078—Shock-testing of vehicles
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
- G01M3/24—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using infrasonic, sonic, or ultrasonic vibrations
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
- G01M3/32—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators
- G01M3/3236—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers
- G01M3/3272—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers for verifying the internal pressure of closed containers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
- B60R21/00—Arrangements or fittings on vehicles for protecting or preventing injuries to occupants or pedestrians in case of accidents or other traffic risks
- B60R21/01—Electrical circuits for triggering passive safety arrangements, e.g. airbags, safety belt tighteners, in case of vehicle accidents or impending vehicle accidents
- B60R21/013—Electrical circuits for triggering passive safety arrangements, e.g. airbags, safety belt tighteners, in case of vehicle accidents or impending vehicle accidents including means for detecting collisions, impending collisions or roll-over
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
- B60R21/00—Arrangements or fittings on vehicles for protecting or preventing injuries to occupants or pedestrians in case of accidents or other traffic risks
- B60R21/02—Occupant safety arrangements or fittings, e.g. crash pads
- B60R21/16—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags
- B60R21/26—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow
- B60R21/268—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow using instantaneous release of stored pressurised gas
Abstract
Description
- The present invention is directed to diagnostic testing of an occupant restraint system and is particularly directed to a method and apparatus for testing the fluid pressure in a sealed vessel from which pressurized fluid is used to fill an air bag of an occupant restraint system upon the occurrence of a vehicle crash condition.
- Vehicle occupant restraint systems having an actuatable restraining device are well known in the art. One particular type of actuatable restraining device includes an inflatable air bag mounted to inflate within the occupant compartment of the vehicle. The air bag has an associated, electrically actuatable ignitor, referred to as a squib.
- Such occupant restraint systems further include a crash sensor for sensing the occurrence of a vehicle crash condition and for providing an electrical signal indicative of the crash condition. When the crash sensor indicates that the vehicle is in a crash condition, an electric current of sufficient magnitude and duration is passed through the squib for the purpose of igniting the squib. The squib, when ignited, ignites a combustible gas generating composition and/or pierces a vessel of pressurized gas operatively coupled to the air bag, which results in inflation of the air bag.
- Pressurized gas vessels for use in occupant restraint systems are pressurized to approximately 2000-3000 PSI. Proper inflation of the air bag upon the occurrence of a vehicle crash condition is dependent on the pressurized vessel being at the proper pressure. Since the pressurized vessel will be installed in the vehicle at the time of manufacture and several years may pass prior to that vehicle being involved in a crash condition, even a small leak in the vessel may leave the vessel with insufficient pressure to inflate the air bag properly during its deployment. It is desirable to provide a diagnostic test arrangement that monitors the fluid pressure in the vessel and warns the vehicle operator when the pressure in the vessel falls below a predetermined minimum value necessary for proper inflation of the air bag.
- A pressurized vessel of an air bag restraint system has a normally sealed air bag opening which is pierced upon firing of the squib and through which fluid flows to the air bag. Several different methods and apparatus have been proposed to measure the pressure within the air bag pressure vessel and to warn the vehicle operator if the pressure falls below a predetermined value. These arrangements typically require that a pressure sensing device have access to the interior of the vessel through an associated test opening in the vessel. The test opening in the vessel is separate from the pierceable sealed air bag opening. If a pressurized vessel leaks, the location of such a leak is most probably at a sealed opening in the vessel. Such leaks may develop simply due to a failure of the seal. Therefore, the more openings that are present in the vessel, the greater the probability that a leak will develop. It is desirable to provide a pressure sensing method and apparatus that does not require an associated opening in the vessel, thereby avoiding an additional potential leak path of pressurized gas from the vessel.
- The present invention provides a method and apparatus for measuring the fluid pressure in a sealed vessel. The invention has particular application for diagnostic testing of a pressurized fluid vessel of an air bag restraint system. In accordance with the invention, a transducer adjacent the vessel outputs an initial square wave pulse to the vessel, a receiver monitors the fluid vibrations, a monitoring circuit monitors for the natural frequency of the fluid and subsequently drives the transducer at the natural frequency of the fluid.
- In accordance with one aspect of the present invention, an apparatus is provided for sensing pressure in a sealed vessel. The apparatus comprises transducer means operatively coupled to the vessel for, when energized, transferring energy to pressurized fluid in the vessel. The energy transferred establishes oscillations of the pressurized fluid in the vessel. Receiver means is operatively coupled to the vessel for providing a received electrical signal having a frequency value indicative of the oscillation frequency of the pressurized fluid in the vessel. Receiver circuit means is operatively connected to the receiver means for providing a fluid resonating signal having a frequency indicative of the natural frequency of the oscillating pressurized fluid in the vessel. The natural frequency is indicative of the fluid pressure in the vessel. The apparatus further includes drive circuit means operatively connected to the receiver circuit means and to the transducer means for initially driving the transducer means with a square wave energy signal. Subsequently, the drive circuit means drives the transducer means with an energy wave having a frequency equal to the natural frequency of the pressurized fluid in the vessel.
- In accordance with another aspect of the present invention, a method is provided for sensing pressure in a sealed vessel. The method comprises the step of transferring energy to pressurized fluid in the vessel. The energy establishes oscillations of the pressurized fluid in the vessel. The method also includes the step of receiving a signal from the vessel having a frequency value indicative of the oscillating frequency of the pressurized fluid in the vessel resulting from the transferred energy including the natural frequency of the fluid. Another step of the method is providing a fluid resonating signal having a frequency equal to the natural frequency of the oscillating pressurized fluid in the vessel. The natural frequency is indicative of the fluid pressure in the vessel. The method further includes initially transferring a square wave energy signal to the vessel, and subsequently transferring an oscillating energy wave to the vessel having a frequency equal to the natural frequency of the pressurized fluid in the vessel.
- In accordance with yet another aspect of the present invention, an air bag diagnostic apparatus is provided for use in an air bag restraint system. The air bag restraint system includes a crash sensor connected to a controller for providing a signal upon the occurrence of a vehicle crash condition. The restraint system also includes a pressurized fluid bottle, a squib connected to the fluid bottle and electrically connected to the controller, and an air bag connected to the fluid bottle. The controller actuates the squib upon the occurrence of a crash condition to pierce a seal on the fluid bottle and let the pressurized fluid in the bottle inflate the air bag. The air bag diagnostic apparatus comprises transducer means operatively coupled to said fluid bottle for, when energize, transferring energy to pressurized fluid in the fluid bottle. The transferred energy establishes oscillations of the pressurized fluid in the fluid bottle. Receiver means is operatively coupled to the fluid bottle for providing a received electrical signal having a frequency value indicative of the oscillation frequency of the pressurized fluid in the vessel. Receiver circuit means is operatively connected to the receiver means for providing a fluid resonating signal having a frequency indicative of the natural frequency of the oscillating pressurized fluid in the fluid bottle. The natural frequency is indicative of the fluid pressure in the fluid bottle. The apparatus further includes drive circuit means operatively connected to the receiver circuit means and to the transducer means for initially driving the transducer means with a square wave energy pulse signal. Subsequently, the drive circuit means drives the transducer means with an oscillating energy wave having a frequency equal to the natural frequency of the pressurized fluid in the fluid bottle. Monitoring means is provided for monitoring the natural frequency of the fluid in the gas bottle and for determining the fluid pressure of the fluid in the fluid bottle in response to the sensed natural frequency. The apparatus further includes means for providing an indication to the vehicle operator if the determined fluid pressure in the fluid bottle is less than a predetermined value.
- Other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from a reading of the following detailed description of preferred embodiments with reference to the accompanying drawings, in which:
- Fig. 1 is a schematic block diagram of an air bag restraint system including a diagnostic arrangement made in accordance with the present invention;
- Fig. 2 is a graphical representation of the amplitude output of the monitored oscillations from the vessel shown in Fig. 1 as a function of a sweep frequency applied to the speaker;
- Fig. 3 is an overlaid graphical representation of (i) relative phase versus input frequency and (ii) signal amplitude versus input frequency for the system shown in Fig. 1;
- Fig. 4 is a graphical representation of natural frequency versus pressure for the system shown in Fig. 1; and
- Fig. 5 is a graphical representation of the speed of sound of the fluid versus pressure for the system shown in Fig. 1.
- Referring to Fig. 1, an air
bag restraint system 20 includes anair bag 22 mounted in an appropriate location such as the steering wheel for the driver or the instrument panel or dashboard for a passenger, so that it will inflate into the vehicle interior compartment. A sealed stiffwalled vessel 30 contains pressurized fluid and is connected to theair bag 22. Asquib 34 is operatively connected to the sealedopening 36 of thevessel 30. When thesquib 34 is ignited, the seal in the opening of the vessel is pierced. When the seal of the vessel is pierced, the pressurized fluid, which may be a gas such as nitrogen or argon, in thevessel 30 passes into and inflates theair bag 22. - The
squib 34 is connected to acontroller 40 such as a microcomputer. Thecontroller 40 is connected to avehicle crash sensor 44. Thecrash sensor 44 can be any of several known types. For example, thecrash sensor 44 may be a mechanical inertia switch, such as a rolamite sensor, or an electrical accelerometer. If a normally open mechanical inertia switch is used, the electrical contacts are normally open during a non-crash condition. If a crash condition occurs, the normally open contacts close. Therefore, closure of the switch contacts is indicative of the occurrence of a vehicle crash condition. - If an electrical accelerometer is used as the
crash sensor 44, there are several known ways of determining if a crash condition is occurring from the accelerometer output signal. One method is to compare the integrated amplitude of the accelerometer signal against a predetermined value. If the value of the integrated accelerometer signal reaches the predetermined value or remains at or above the predetermined value for a predetermined time, this is an indication that a crash condition is occurring. Once thecontroller 40 determines that a vehicle crash is occurring for which deployment of the air bag is necessary to protect the vehicle occupants, thecontroller 40 ignites thesquib 34. - A
diagnostic circuit 50 is operatively connected to thevessel 30 and to thecontroller 40. The diagnostic circuit determines the natural frequency of the gas in thevessel 30. The natural frequency of the gas in the vessel is functionally related to the pressure of the gas in thevessel 30. - A
speaker 60 is operatively connected to thevessel 30. The speaker is a coil and magnet system that drives a thin flat stainless steel diaphragm. The lines of flux are directed through the center of the coil and pass through the stainless steel diaphragm. The steel diaphragm moves in response to the magnetic field of the coil. The diaphragm thickness is preferably 1 millimeter. The coils are preferably made of 32 awg wire with approximately 250 turns with a DC resistance of 150 Ohms. Energy produced by thespeaker 60 is transferred to the pressurized fluid or gas in thevessel 30. - A
piezoelectric capacitive sensor 62 is operatively connected to thevessel 30. Thesensor 62 picks up the vibrations of the pressurized fluid in the vessel with the charge across the capacitive sensor changing as a function of the detected vibrations. Although polyvinylidine fluoride may be used as a piezoelectric material for thesensor 62, its low mechanical coupling coefficient makes other arrangements more desirable. Preferably, piezoelectric material, such as zinc oxide, is sputtered in a thin film onto a bulk sheet of stainless steel diaphragm material. The sensor electrodes are preferably sputtered aluminum. Polyamide is applied as a protective passivation layer. - The
sensor 62 is electrically connected to a current-to-voltage converter 70 for the conversion of the electrical current output from thecapacitive sensor 62 into a voltage signal. The current-to-voltage converter 70 includes an operational amplifier ("op amp") 72 having its invertinginput 74 connected to thesensor 62. Theoutput 78 ofop amp 72 is connected to the invertinginput 74 through a parallel combination of afeedback resistor 80 andcapacitor 82. Anon-inverting input 84 of theop amp 72 is connected to electrical ground. - The component values for
capacitor 82 and theresistor 80 are selected to give a desired phase shift. Preferably, the values are selected to provide a phase shift of + 45 degrees. - The output of the current-to-
voltage converter 70 is connected to anamplifier circuit 90. Theamplifier circuit 90 includes anserial input resistor 92 that connects the output of the current-to-voltage converter 70 to the invertinginput 94 of anop amp 96. Theoutput 98 of theop amp 96 is connected to its invertinginput 94 through afeedback resistor 100. Thenon-inverting input 102 of theop amp 96 is connected to electrical ground. The values of theresistors amplifier 90 is greater than one. Because theamplifier 90 provides an inverting gain, the signal from the current-to-voltage converter is phase shifted by 180 degrees byamplifier 90. - The output of the
amplifier 90 is connected to alow pass filter 110. The purpose for thelow pass filter 110 is to remove harmonics of the pressure resonant or natural frequency of the pressurized fluid as well as frequencies that may be present as a result of vibrations of thevessel 30 itself. Any of several types of low pass filters may be used such as Butterworth, Chebychev, Bessel, or Elliptic. A simple RC filter may be used, as shown in Fig. 1. Such an RC filter includes aresistor 112 and acapacitor 114. The output of thelow pass filter 110 is present at the junction ofresistor 112 andcapacitor 114. The output signal of the low pass filter has a frequency value equal to the natural frequency of the pressurized fluid in thevessel 30, which, in turn, is functionally related to the pressure of the fluid. Thelow pass filter 110 provides an additional 180 degree phase shift in the signal output from theamplifier 90. - The output of the low
pass filter circuit 110 is connected to a voltage-to-current converter 120. The voltage-to-current converter 120 includes afirst op amp 122 having itsnon-inverting input 124 connected to the output of thelow pass filter 110. Theoutput 126 of theop amp 122 is connected to itsinverting input 128. Theoutput 126 of theop amp 122 is also connected to thenon-inverting input 130 of anop amp 132. The invertinginput 134 of theop amp 132 is connected to electrical ground through aresistor 136. Theoutput 138 of theop amp 132 is controllably connected to thebase 140 of atransistor 142. Thecathode 144 of thetransistor 142 is connected to a voltage source Vcc. Theelectrode 146 of thetransistor 142 is connected to afirst terminal 150 of thespeaker 60. Asecond terminal 152 of thespeaker 60 is connected to the junction of theresistor 136 and the invertinginput 134 of theop amp 132. Because the voltage-to-current converter 120 is non-inverting, there is no phase shift between its input and output. The value ofresistor 136 controls the power supplied to the speaker. - The output of the
low pass filter 110 is also connected to thecontroller 40. Thecontroller 40 monitors the frequency of the output signal from thelow pass filter 110. Thecontroller 40 also uses an internal look- up table to determine the pressure of the fluid in thevessel 30 from the frequency value. If the pressure falls below a predetermined minimum value at any time during operation of the vehicle, thecontroller 40 actuates a warning indicator 153 which is mounted in the vehicle interior. The actuated indicator 153 informs the vehicle operator that a problem exists in the air bag system, i.e., the fluid pressure in thevessel 30 is too low. - Each of the
op amps terminal 160 of a solidstate switching device 164 such as a field-effect-transistor ("FET"). Asecond terminal 166 of theFET 164 is connected to the voltage source Vcc. Thecontroller 40 is controllably connected to theswitch control input 168 of theFET 164. After the vehicle ignition is first started, the controller switches theFET 164 ON, thereby connecting Vcc to each of theop amps speaker coil 60. Those skilled in the art will appreciate that a square wave comprises the sum of all frequency components. Therefore, all frequency values are present in a single square wave pulse. When the square wave pulse "hits" the vessel, the pressurized gas inside of the vessel will ring at its natural frequency, which is functionally related to the pressure of the fluid. - The circuit loop comprising the
sensor 62, the current-to-voltage converter 70, theamplifier 90, thelow pass filter 110, the voltage-to-current converter 120, and thespeaker 60, which form a phase lock circuit having loop feedback, initially has a phase shift of +45 degrees. If a natural frequency exists in the pressurized fluid when thespeaker 60 is initially pulsed with a square wave signal, the natural frequency pulls the loop phase shift down to a value of 0. At resonance, there is a phase shift between thespeaker 60 and thereceiver 62 of -45 degrees. Once the phase shift of the loop reaches the 0 value, the loop locks on to that frequency because the two conditions of loop oscillation are satisfied, i.e., a phase shift of 0 degrees and a gain greater than one. The natural frequency of the fluid as detected by the loop is monitored at the output from thelow pass filter 110. This frequency is, through the feed-back circuit, used to drive thespeaker 60 and continues to drive thespeaker 60 at the natural frequency for a predetermined time period as determined bycontroller 40. Those skilled in that art will appreciate that the circuit arrangement may be left on continuously or can operate for a predetermined time after vehicle ignition ON. - The natural frequency of the compressed gas in the
vessel 30 is the mechanical equivalent of an electrical oscillation. The only difference between the two is that the mechanical oscillation cannot be sustained at the same amplitude from cycle to cycle due to a finite amount of viscous damping in the system. However, the electrical loop of the present invention amplifies and phase shifts the natural frequency (brings the loop to 0 phase shift), thereby to sustain the oscillations. - A better understanding of the natural frequency of the fluid in the vessel can be appreciated from the graph shown in Fig. 2. In this graph, the magnitude of the signal from the
sensor 62 is on the Y-axis and frequency is on the X-axis. To develop this graph, thespeaker 60 is driven by an oscillator (not shown) that sweeps through a frequency range from 750 Hz to 1000 Hz. The drive signal for the speaker is a fixed amplitude signal. The graph represents data from a pressurized vessel having an inert noble gas at 2000 PSI. As can be seen from the graph, the magnitude of the oscillations seen by the sensor is greatest at approximately 870 Hz. This translates into a very small damping coefficient at 870 Hz, which means that the natural frequency of the gas is 870 Hz. - If this pressurized vessel was monitored by the control loop of the present invention, the loop would lock onto the 870 Hz frequency. The initial square wave pulse from the speaker has all frequencies present, including 870 Hz. The initial application of the square wave pulse would result in the sensor detecting the oscillation of greatest amplitude, i.e., the 870 Hz frequency. The control loop is designed so as not to saturate electrically, thereby permitting the loop to oscillate at a single sinusoidal frequency due to the extremely high Q of the natural frequency of the gas in the vessel. Also, the loop satisfies the two conditions need for oscillation at the natural frequency of the gas, i.e., a gain greater than one and a zero phase shift.
- Referring to Fig. 3, a phase versus frequency graph is superimposed upon an amplitude versus frequency graph. Frequency is on the X-axis. The Y-axis has both a phase designation and an amplitude designation. The phase values of the phase graph represents the value of the signal output from the
low pass filter 110 divided by the value of the input signal to thespeaker 60. The frequency at which the peak amplitude occurs and at which the zero phase occurs is the natural frequency of the pressurized gas in the vessel. Rather than sweeping through a frequency range, "hitting" the vessel with the initial square wave energy pulse which includes all of the frequencies results in the natural frequency being picked up by thesensor 62 and the frequency being locked-on by the circuit loop. - Fig. 4 is a natural frequency versus pressure graph with frequency on the Y-axis and pressure in PSI on the X-axis. This graph shows the functional relationship between frequency and pressure for an inert noble gas.
- Fig. 5 is a speed of sound in the pressurized fluid versus pressure graph with the speed of sound on the Y-axis and pressure in PSI on the X-axis. This graph is also for an inert noble gas. As can be seen by the graph, the speed of sound in the gas increases as the pressure of the gas increases. The circuit loop of the present invention exploits this phenomena by locking onto the natural frequency of the pressurized gas in the vessel due to the gas resonating in the vessel.
- The natural frequency of the gas in the vessel is governed by a second order system assuming lumped parameters. Using a basic spring-mass model, the laws of motion may be expressed as:
- A
temperature sensor 170 is connected to thecontroller 40. In accordance with the well known "Ideal Gas Law," the pressure of the gas in thevessel 30 increases with an increase in the temperature of the gas. Since the ambient temperature affects the temperature of the gas in thevessel 30, it is necessary to monitor the gas temperature and to adjust the determination of the gas pressure as a function of the sensed temperature. Thecontroller 40 measures the frequency output from thelow pass filter 110 and adjusts the measurement based upon the monitored temperature. Thetemperature sensor 170 can either monitor the ambient temperature or can be secured to the vessel to measure the vessel temperature more accurately. The temperature of the gas is functionally related to the temperature of the vessel which is, in turn, functionally related to the ambient temperature about the vessel. - This invention has been described with reference to preferred embodiments. Modifications and alterations may occur to others upon reading and understanding this specification. It is our intention to include all such modifications and alterations insofar as they come within the scope of the appended claims and the equivalents thereof.
- It should be noted that the objects and advantages of the invention may be attained by means of any compatible combination(s) particularly pointed out in the items of the following summary of the invention and the appended claims.
- 1. An apparatus for sensing pressure in a sealed vessel, said apparatus comprising:
- transducer means operatively coupled to said vessel for, when energized, transferring energy to pressurized fluid in said vessel, said transferred energy establishing oscillations of the pressurized fluid in the vessel;
- receiver means operatively coupled to said vessel for providing a received electrical signal having a frequency value indicative of a natural frequency of the pressurized fluid in said vessel;
- receiver circuit means operatively connected to said receiver means for providing a fluid resonating signal having a frequency equal to the natural frequency of the oscillating pressurized fluid in the vessel, the natural frequency being indicative of the fluid pressure in said vessel; and
- drive circuit means operatively connected to said receiver circuit means and to said transducer means for initially driving said transducer means with a square wave energy pulse signal and subsequently driving said transducer means with an oscillating energy wave having a frequency equal to said natural frequency of said pressurized fluid in said vessel.
- 2. The apparatus wherein said receiver circuit means includes filtering means for filtering said received electrical signal to remove frequency components that result from oscillations of the vessel itself, said fluid resonating signal being output from said filtering means so that the frequency of said fluid resonating signal is due only to the pressurized fluid in the vessel.
- 3. The apparatus wherein said filtering means includes a low-pass filter.
- 4. The apparatus wherein said receiver circuit means further includes a capacitive piezoelectric sensor that outputs an electrical current signal.
- 5. The apparatus wherein said receiver circuit means further includes a current-to-voltage converter circuit connected to said sensor for converting said current signal from said sensor into a voltage signal.
- 6. The apparatus wherein said filtering means is a low-pass filter.
- 7. The apparatus further including monitoring means for monitoring the natural frequency of the fluid in said vessel and for determining the fluid pressure of the fluid in the vessel in response to the sensed natural frequency and means for providing an indication if the determined fluid pressure is less than a predetermined value.
- 8. The apparatus further including a temperature sensing means connected to said monitoring means for providing a signal to said monitoring means indicative of the ambient temperature around said vessel, said monitoring means adjusting the indication of tile fluid pressure in said vessel in response to the sensed temperature.
- 9. The apparatus wherein said transducer means is a speaker.
- 10. The apparatus wherein said transducer means, said receiver means, said receiver circuit means, and said drive circuit means form a closed control loop, said closed control loop including means for providing a loop gain of greater than one and a phase shift of zero degrees upon the occurrence of a natural frequency of the pressurized fluid so that said closed control loop locks onto said natural frequency.
- 11. An air bag diagnostic apparatus for use in an air bag restraint system including a crash sensor connected to a controller for providing a signal upon the occurrence of a vehicle crash condition, a pressurized fluid bottle, a squib connected to the fluid bottle and electrically connected to the controller, and an air bag connected to the fluid bottle, the controller actuating the squib upon the occurrence of a crash condition to pierce a seal on the fluid bottle and let the pressurized fluid in the bottle inflate the air bag, the diagnostic apparatus comprising:
- transducer means operatively coupled to said fluid bottle for, when energized, transferring energy to pressurized fluid in said fluid bottle, said energy establishing oscillations of the pressurized fluid in the fluid bottle;
- receiver means operatively coupled to said fluid bottle for providing a received electrical signal having a frequency value indicative of the oscillation frequency of the pressurized fluid in said fluid bottle;
- receiver circuit means operatively connected to said receiver means for providing a fluid resonating signal having a frequency indicative of the natural frequency of the oscillating pressurized fluid in the fluid bottle, the natural frequency being indicative of the fluid pressure in said fluid bottle;
- drive circuit means operatively connected to said receiver circuit means and to said transducer means for initially driving said transducer means with a square wave energy pulse signal and subsequently driving said transducer means with an oscillating energy wave having a frequency equal to said natural frequency of said pressurized fluid in said fluid bottle;
- monitoring means for monitoring the natural frequency of the fluid in said fluid bottle and determining the fluid pressure of the fluid in the fluid bottle in response to the sensed natural frequency; and
- means for providing an indication to the vehicle operator if the determined fluid pressure in the fluid bottle is less than a predetermined value.
- 12. The apparatus further including a temperature sensing means connected to said monitoring means for providing a signal to said monitoring means indicative of the ambient temperature around said vessel, said monitoring means adjusting the indication of the fluid pressure in said fluid bottle in response to the sensed temperature.
- 13. The apparatus wherein said receiver circuit means includes filtering means for filtering said received electrical signal to remove frequency components that result from oscillations of the fluid bottle itself, said fluid resonating signal being output from said filtering means so that the frequency of said fluid resonating signal is due only to the pressurized fluid in the fluid bottle.
- 14. The apparatus wherein said filtering means includes a low-pass filter.
- 15. The apparatus wherein said receiver circuit means further includes a capacitive piezoelectric sensor that outputs an electrical current signal.
- 16. Tile apparatus wherein said receiver circuit means further includes a current-to-voltage converter circuit connected to said sensor for converting said current signal from said sensor into a voltage signal.
- 17. The apparatus wherein said filtering means is a low-pass filter.
- 18. The apparatus wherein said transducer means is a speaker.
- 19. The apparatus wherein said transducer means, said receiver means, said receiver circuit means, and said drive circuit means form a closed control loop, said closed control loop including means for providing a loop gain of greater than one and a phase shift of zero degrees upon the occurrence of a natural frequency of the pressurized fluid so that said closed control loop locks onto said natural frequency.
- 20. An apparatus for sensing pressure in a sealed vessel, said apparatus comprising:
- transducer means operatively coupled to said vessel for, when energized, transferring a square wave energy pulse to pressurized fluid in said vessel, said transferred square wave energy pulse establishing oscillations of the pressurized fluid in the vessel including a frequency value equal to the natural frequency of the pressurized fluid;
- receiver means operatively coupled to said vessel for providing a received electrical signal having a frequency value indicative of the natural frequency of the pressurized fluid in said vessel; and
- receiver circuit means operatively connected to said receiver means for providing a fluid resonating signal having a frequency equal to the natural frequency of the oscillating pressurized fluid in the vessel, the natural frequency being indicative of the fluid pressure in said vessel, said receiver circuit means including filtering means connected to said receiver means for removing frequency components from said received electrical signal that result from oscillations of the vessel itself.
- 21. A method for sensing pressure in a vessel, said method comprising the steps of:
- transferring energy to pressurized fluid in the vessel, said transferred energy establishing oscillations of the pressurized fluid in the vessel;
- receiving a signal from the vessel having a frequency value indicative of the oscillation frequency of the pressurized fluid in said vessel including the natural frequency of the pressurized fluid in said vessel;
- providing a fluid resonating signal having a frequency equal to the natural frequency of the oscillating pressurized fluid in the vessel, the natural frequency being indicative of the fluid pressure in said vessel;
- initially providing a square wave energy pulse signal to said vessel; and
- subsequently providing an oscillating energy wave having a frequency equal to said natural frequency of said pressurized fluid in the vessel.
- 22. The method further including the step of filtering the received electrical signal to remove frequency components that result from oscillations of the vessel itself so that the frequency of said fluid resonating signal is due only to the pressurized fluid in the vessel.
- 23. The method wherein said step of filtering includes passing frequency components less than a predetermined value.
- 24. The method wherein said step of receiving includes providing a capacitive piezoelectric sensor that outputs an electrical current signal.
- 25. The method wherein said step of receiving further includes providing a current-to-voltage converter circuit connected to said sensor for converting said current signal from said sensor into a voltage signal.
- 26. The method wherein said step of filtering means includes passing only frequency components having a value less than a predetermined value.
- 27. A method for determining the functionality of an air bag restraint system including a crash sensor connected to a controller for providing a signal upon the occurrence of a vehicle crash condition, a pressurized fluid bottle, a squib connected to the fluid bottle and electrically connected to the controller, and an air bag connected to the fluid bottle, the controller actuating the squib upon the occurrence of a crash condition to pierce a seal on the fluid bottle and let the pressurized fluid in the bottle inflate the air bag, the method comprising the steps of:
- transferring energy to pressurized fluid in said vessel from a transducer means, said transferred energy establishing oscillations of the pressurized fluid in the fluid bottle;
- providing a received electrical signal having a frequency value indicative of the oscillation frequency of the pressurized fluid in said fluid bottle including the natural frequency of the pressurized fluid in the vessel;
- providing a fluid resonating signal having a frequency equal to of the natural frequency of the oscillating pressurized fluid in the vessel, the natural frequency being indicative of the fluid pressure in said fluid bottle;
- initially providing a square wave energy pulse signal to the fluid bottle;
- subsequently providing an oscillating energy wave to the fluid bottle having a frequency equal to said natural frequency of said pressurized fluid in said fluid bottle;
- monitoring the natural frequency of the fluid in said fluid bottle;
- determining the fluid pressure of the fluid in the fluid bottle in response to the sensed natural frequency; and
- providing an indication to the vehicle operator if the determined fluid pressure in the fluid bottle is less than a predetermined value.
- 28. The method further including the steps of sensing the ambient temperature around the fluid bottle and adjusting the indication of the fluid pressure in said fluid bottle in response to the sensed temperature.
- 29. The method further including the step of filtering the received electrical signal to remove frequency components that result from oscillations of the fluid bottle itself so that the frequency of said fluid resonating signal is due only to the pressurized fluid in the fluid bottle.
- 30. A method for sensing pressure in a vessel, said method comprising the steps of:
- transferring a square wave energy pulse to pressurized fluid in the vessel, said transferred energy establishing oscillations of the pressurized fluid in the vessel including a frequency value equal to the natural frequency of the pressurized fluid;
- receiving a signal from the vessel having a frequency value indicative of the oscillation frequency of the pressurized fluid in said vessel including the natural frequency of the pressurized fluid in said vessel;
- filtering the signal received from the vessel to remove frequency components that result from oscillations of the vessel itself; and
- providing a fluid resonating signal in response to the filtered received signal having a frequency equal to the natural frequency of the oscillating pressurized fluid in the vessel, the natural frequency being indicative of the fluid pressure in said vessel.
Claims (12)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US07/986,035 US5351527A (en) | 1992-12-04 | 1992-12-04 | Method and apparatus for testing fluid pressure in a sealed vessel |
US986035 | 1992-12-04 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0600491A2 true EP0600491A2 (en) | 1994-06-08 |
EP0600491A3 EP0600491A3 (en) | 1995-08-02 |
EP0600491B1 EP0600491B1 (en) | 1998-08-05 |
Family
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP93119457A Expired - Lifetime EP0600491B1 (en) | 1992-12-04 | 1993-12-02 | Method and apparatus for testing fluid pressure in a sealed vessel |
Country Status (4)
Country | Link |
---|---|
US (1) | US5351527A (en) |
EP (1) | EP0600491B1 (en) |
JP (1) | JPH06213749A (en) |
DE (1) | DE69320153D1 (en) |
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Cited By (5)
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Also Published As
Publication number | Publication date |
---|---|
JPH06213749A (en) | 1994-08-05 |
US5351527A (en) | 1994-10-04 |
DE69320153D1 (en) | 1998-09-10 |
EP0600491A3 (en) | 1995-08-02 |
EP0600491B1 (en) | 1998-08-05 |
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